The invention relates to a  less than  less than Moineau greater than  greater than  type progressive-cavity pump comprising a stator consisting of at least two parts. A first part consists of a material of low elasticity, allowing notably to retain the properties of a second part. The second part is suited to provide a sufficient stress exerted by the first part on the rotor and to obtain a pressure gain required for pumping operations.
The invention is notably applied for pumping all types of hydrocarbons or aggressive products.
Progressive-cavity pumps, or Moineau type pumps, are well-known and their method of operation has been widely described in the prior art. The pump comprises an internal gear or rotor, and an external gear or stator. Each gear has a longitudinal axis, the axes being parallel and distant from one another. The stator has one more tooth than the rotor, the latter is such that its teeth are constantly in contact with the stator. The ratio of the spiral pitch of the rotor to that of the stator is proportional to the corresponding ratio of the number of teeth of the two gears. The helical winding of the gear teeth around their axis of rotation creates, between the two gears, a volume whose length is equal to the pitch of the external gear. Provided that the spirals of the external and internal gears exhibit more than one turn, this gear layout and the respective motion thereof form closed cavities. The pump this created allows discharge of a volume of fluid under pressure without non-return valve.
In order to obtain satisfactory pressure heads, the cavities formed between the rotor and the stator must be closed with a certain sealing level. Sealing is notably provided by a negative clearance between the diameter of the section of the rotor and the dimension of the stator teeth. Maintenance of this negative clearance is provided by a certain elasticity of the rotor and/or of the stator. In order to avoid an efficiency loss notably due to the mechanical friction between the stator and the rotor as they rotate, it is wellknown to use a stator made of an elastomer and a rotor made of metal.
Moineau type pumps are well-suited for pumping certain petroleum effluents, notably viscous crudes, in well bottoms or at the surface. However, the composition of crudes known as  less than  less than light  greater than  greater than  causes a chemical degradation of elastomers, which requires stator servicing and therefore leads to an increase in the maintenance and production costs. For effluents having temperatures above 140xc2x0 C., the elastomer undergoes thermal degradation. Such a degradation can also exist when pumping a fluid with a high gas/liquid ratio as a result of heating of the gas by compression.
High temperatures or temperature rises during operation can also cause problems of adhesion of the elastomer to the metallic barrel of the pump and lead to detachment of the elastomeric part of the stator from the pump barrel.
Pumping of crudes having high temperatures, at great depths or in wells stimulated by heat for example, and pumping of effluents with a high gas proportion, under surface conditions for example, is therefore not always accessible to Moineau pumps.
The object of the present invention is an improvement of a  less than  less than Moineau  greater than  greater than type pump. The stator is a  less than  less than composite  greater than  greater than element. The word  less than  less than composite  greater than  greater than is used in the present description to designate the structure in at least two parts of the stator. A first part of the stator is made of a material of low elasticity, such as a metal, and a second part, in contact with the pump barrel, is selected to obtain and maintain a stress exerted by the first part on the rotor so as to generate the desired pressure gain.
The invention relates to a progressive-cavity pump intended to impart energy to a fluid, said pump comprising at least a casing, a stator and a rotor, said rotor being arranged in said stator.
It is characterized in that the stator consists of at least two parts, a first part being made of a material of low elasticity, and a second part located between the inner wall of the casing and the first part, said second part being suited to apply and/or to maintain a stress a exerted by the first part on the rotor in order to obtain the pressure gain required for the pumped fluid.
The first part can be made of a material allowing to preserve the properties of the second part.
The first part is for example made of a metal.
The second part can be made of an elastomer.
The second part is for example made from a metallic network embedded in an elastomer matrix.
The second part consists for example, totally or partially, of a fluid having a sufficient pressure for applying a required stress exerted by the first part on the rotor.
The fluid under pressure can be part of the pumped fluid.
The invention also relates to a process for manufacturing a stator consisting of at least a first part in contact with a rotor and of a second part, and intended to be used in a progressive-cavity pump.
The process is characterized in that it comprises at least the following stages:
1) placing a mandrel whose shape is selected according to the first part of the stator inside an element made from a metallic material, the assembly itself being placed in a housing provided with one or more openings,
2) applying to the element a sufficient pressure for shaping of the element, so that it moulds to the mandrel so as to form said first part, and
3) removing the mandrel.
During stage 2), a fluid under pressure can be injected between the housing and the element.
A polymerizable material is for example injected into the space formed by the housing and the outer wall of the element and the assembly is subjected to a polymerization stage so as to form the second part of the stator.
An adhesive material is for example injected prior to injecting the polymerizable material.
Means allowing heat dissipation are for example positioned between the housing and the element prior to injecting the polymerizable material and/or to centering the part in relation to the casing.
The pump and the process according to the invention are applied for pumping of a petroleum effluent or of aggressive fluids.
The pumping device according to the invention notably allows to extend the pumping range to a wider hydrocarbon range and to increase the life of the equipment.